Embryology of the Reproductive Tracts

Question 1

When is the sex of an embryo determined?

Answer 1

At fertilization by the sperm (X or Y) that fertilizes the oocyte

Question 2

When do male and female characteristics begin to develop?

Answer 2

The seventh week; undifferentiated from weeks 1-6

Question 3

At what week do the genitalia begin to have male and female characteristics?

Answer 3

Week 10

Question 4

At what week is the phenotypic differentiation complete?

Answer 4

Week 20

Question 5

At the end of the 3rd week what do cells from the primitive streak form?

Answer 5

Paraxial mesoderm

Question 6

What are the layers of the mesoderm from medial to lateral?

Answer 6

Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm

Question 7

What is the mesoderm primarily responsible for?

Answer 7

Formation of the kidneys and internal genitalia and their ducts

Question 8

Where does the urogenital ridge form?

Answer 8

On each side of the dorsal mesentery forming the nephrogenic and genital ridge

Question 9

What gives rise to the urinary system?

Answer 9

The nephrogenic ridge

Question 10

What gives rise to the genital system?

Answer 10

Genital (gonadal) ridge

Question 11

What are the three slightly overlapping kidney systems formed from cranial to caudal?

Answer 11

Pronephros
Mesonephros
Metanephros

Question 12

What do the mesonephros arise from and when?

Answer 12

Intermediate mesoderm

Beginning of the fourth week mesonephric tubules appear

Question 13

Where do the mesonephric tubules run?

Answer 13

Into the longitudinal wolffian duct

Question 14

What are primordial germ cells?

Answer 14

Spherical sex cells that are recognizable at week 5

Question 15

What are the two pair of genital ducts both male and female have initially?

Answer 15

Wolffian (mesonephric)

Paramesonephric (Mullerian)

Question 16

What do the two wolffian and Mullerian ducts come together to form?

Answer 16

Uterine canal

Question 17

What off the Wolffian and Mullerian ducts remain in each sex?

Answer 17

Wolffian: male
Mullerian: female

Question 18

What do the indifferent gonads consist of?

Answer 18

External cortex (mesothelial cells with primordial germ cell)
Internal medulla

Question 19

What are the primitive sex cords?

Answer 19

When the mesothelium of the genital ridge proliferates and cells penetrate the underlying mesenchyme in the medulla (mesothelial cells dive into the cortex)

Question 20

At what week are the two sexes still identical and called indifferent gonads?

Answer 20

Seventh week

Question 21

What does male phenotype develop?

Answer 21

Seventh week

Question 22

What gene is needed for males to become males?

Answer 22

SRY gene on the short arm of the Y chromosome

Question 23

What does SRY gene code for?

Answer 23

Testis-determining factor (TDF)

Question 24

Under influence of TDF what do primitive sex cords in the medulla become?

Answer 24

Differentiate into seminiferous tubules

Question 25

What does SRY activate aside from TDF?

Answer 25

Sox-9 gene a testis-specific enhancer | Inhibits Wnt4

Question 26

What does Wnt4 do?

Answer 26

Wnt4 inhibits Sox-9

Question 27

What does the absence of a Y chromosome result in?

Answer 27

Default formation of ovaries

Question 28

What does development of female phenotype require?

Answer 28

Two X chromosomes

Question 29

When does ovarian development begin?

Answer 29

12th week of development

Question 30

What gene is needed for female development?

Answer 30

Wnt4

Question 31

What does Wnt4 gene do?

Answer 31

Inhibits Sox-9 | Activates Dax1

Question 32

What do Sox-9 and Dax1 work on?

Answer 32

Genital ridge to form testis and ovaries respectively

Question 33

What occurs to the medulla and cortex in males?

Answer 33

Medulla develops | Cortex degenerates

Question 34

What occurs to the medulla and cortex in females?

Answer 34

Medulla degenerates | Cortex develops

Question 35

In males, what do the mesonephric ducts give rise to?

Answer 35

Tubules of the rete testis and efferent ducts

Question 36

In the fourth month of male development what do the primitive sex cords give rise to?

Answer 36

Sertoli cells

Question 37

What do the Sertoli cells secrete?

Answer 37

AMH (anti-Mullerian hormone)

Question 38

What occurs to seminiferous cords?

Answer 38

They remain solid until puberty then become seminiferous tubules

Question 39

What forms the ovarian medulla?

Answer 39

Primitive sex cords dissociate into irregular cell clusters, later disappear and are replaced by vascular stroma

Question 40

What are cortical cords?

Answer 40

Second generation of cords that proliferate in the seventh week from mesothelium

Question 41

Where are mesothelium cells found?

Answer 41

In the cortex of the genital ridge (inside is the mesenchyme)

Question 42

What do the cortical cords do?

Answer 42

Penetrate the underlying mesenchyme

Question 43

What do the cortical cords become?

Answer 43

Differentiate into follicular cells wrapping around a primordial germ cell (primordial follicle)

Question 44

Why do the testis descend?

Answer 44

Due to the disproportionate growth of the upper abdominal region away from the pelvic region

Question 45

What is the gubernaculum?

Answer 45

Band of fibrous tissue along the posterior wall that extends from the caudal pole of the testes to the scrotum

Question 46

What do the remnants of the gubernaculum serve of as an adult?

Answer 46

Anchor the testes within the scrotum

Question 47

What does the peritoneum alongside the gubernaculum form?

Answer 47

Processus vaginalis

Question 48

What exactly is the processus vaginalis?

Answer 48

The out pouching of the peritoneum or the trail the testes leave behind as they descend until it closes

Question 49

At the distal end, the processus vaginalis remains, what is it called?

Answer 49

Tunica vaginalis of the testes

Question 50

What is failure of the testes to descend called?

Answer 50

Bilateral undescended testes (cryptorchidism)

Question 51

What is failure of the processus vaginalis to close called?

Answer 51

Hydrocele of the testes

Question 52

What occurs if the deep ring is too loose?

Answer 52

Congenital inguinal hernia

Question 53

What converts testosterone to DHT?

Answer 53

5-alpha reductase

Question 54

What do testosterone receptor complexes mediate?

Answer 54

Virilization of the mesonephric ducts to form vas deferens, seminal vesicles, efferent ductules, and epididymis

Question 55

What do DHT receptor complexes modulate?

Answer 55

Differentiation of the male external genitalia

Question 56

What does estrogen from the mother do to females?

Answer 56

Stimulates (Mullerian) Paramesonephric ducts to from uterine tubes, uterus, cervix, and upper 1/3 vagina

Question 57

What do the Mullerian and Wolffian ducts form together?

Answer 57

Uterovaginal primordium initially when they are still separate and then fuse to form uterine canal

Question 58

What forms the Uterovaginal primordium (uterine canal)?

Answer 58

Two distal parts of the Paramesonephric ducts (Mullerian)

Question 59

What separates the Uterovaginal primordium?

Answer 59

Uterine septum

Question 60

What does the Uterovaginal primordium give rise to?

Answer 60

Upper 1/3 of the vagina Fundus Body Cervix of the uterus

Question 61

What forms the lower 2/3 of the vagina?

Answer 61

Sinovaginal bulbs proliferate and form a solid vaginal plate

Question 62

What are the vaginal fornices?

Answer 62

Proximal 1/3 of vagina around the end of the uterus and of paramesonephric origin

Question 63

What is the lower 2/3 of the vagina derived from?

Answer 63

Urogenital sinus

Question 64

What are the POTENTIAL remnants of the wolffian duct in females called? (from closest to the ovaries to further away respectively)

Answer 64

Epoophoron | Paroophoron

Question 65

What may a epoophoron form later in life?

Answer 65

May form Gartner's duct and cyst

Question 66

What does the mesonephric duct form in males?

Answer 66

Tail of epididymis, seminal vesicle, ductus deferens

Question 67

What is the role of AMH?

Answer 67

Released from Sertoli cells and causes paramesonephric ducts in males to degenerate except for a small portion at their cranial ends forming the appendix testis

Question 68

What forms on either side of the urethral fold?

Answer 68

Labioscrotal swellings

Question 69

What determines development of external genitalia in males?

Answer 69

DHT

Question 70

What forms the corpora cavernosa and spongiosum in males?

Answer 70

Genital tubercle now called the primordial phallus

Question 71

What determines development of external genitalia in females?

Answer 71

Estrogen

Question 72

What does the primordial phallus cause in males?

Answer 72

Pulls the urethral folds toward each other so that they form the urethral groove

Question 73

What occurs in female to form external genitalia?

Answer 73

Genital tubercle elongates to form clit and bulb of vestibule

Question 74

What occurs to urethral folds in females?

Answer 74

Do not fuse but form the labia minora; labrioscrotal swellings enlarge to for labia majora

Question 75

What does the urogenital groove form in females?

Answer 75

Stays open and forms the vestibule

Question 76

What is failure of urethral folds to close called?

Answer 76

Hypospadias

Question 77

In males what do the urethral folds do?

Answer 77

Close to form penile urethra (urethral groove is before it closes)

Question 78

What does the gubernaculum become in females?

Answer 78

Ovarian ligament | Round ligament of uterus

Question 79

Where do gonads arise from?

Answer 79

Intermediate mesoderm